to add the list, goto the snippets panel:
Window -> Snippets
in the snippets panel select eCart -> Shipping -> UPS Services this will add a list of services to the checkout page.
see this post for details on the protocol for adding a field to the checkout page:
basically, when adding a field to the checkout page, you need to add a set session value behavior and hidden field of the same name to the confirm page.
once that is all in place, edit the shipping rate look up behavior on the confirm page. For the Shipping service, click the lightning bolt and select the Session variable that will be created